1. Field of the Invention
This invention relations to a solid state imaging device.
2. Description of the Related Art
The solid state imaging device shown in FIG. 1 is of the interline transfer type and has horizontal charge transfer elements at the opposite ends of vertical charge transfer elements.
The present conventional example includes, as shown in FIG. 1, first element separation region 701 and second element separation region 705. A plurality of columns of vertical charge transfer element 702 set composed of bidirectionally transferable charge transfer apparatus, photoelectric transform element 703 set individually disposed corresponding to vertical charge transfer elements 702, and bidirectionally transferable first horizontal charge transfer element 704a and second horizontal charge transfer element 704b electrically coupled to the opposite ends of vertical charge transfer elements 702 are provided in first element separation region 701. Meanwhile, first to fourth outputting circuit elements 706a, 706b and 706c, 706d coupled to the opposite ends of horizontal charge transfer elements 704a and element 704b, respectively, are provided in second element separation region 705. Second element separation region 705 is fixed to a reference potential via a metal wiring line at a peripheral portion of the device. It is to be noted that signals outputted from outputting circuit elements 706a, 706b, 706c and 706d are outputted to the outside via output terminals 707a, 707b, 707c and 707d, respectively (refer to Japanese Patent Laid-Open Application No. 1983-195371).
As shown in FIGS. 2a to 2d, in the present conventional example, P-type well layer 802 having an impurity concentration of approximately 5E15 cm.sup.-3 is formed on one principal surface of N.sup.- -type semiconductor substrate 801 having an impurity concentration of approximately 5E14 cm.sup.-3, and first P.sup.+ -type semiconductor region 803 which forms first element separation region 701 and has an impurity concentration of approximately 1E18 cm.sup.-3, second P.sup.+ -type semiconductor region 804 which forms second element separation region 705 and has an impurity concentration of approximately 1E18 cm.sup.-3, N-type semiconductor region 805 which forms vertical charge transfer elements 702 and has an impurity concentration of approximately 1E17 cm.sup.-3, another N-type semiconductor region (not shown) which forms photoelectric transform elements 703 and has an impurity concentration of approximately 5E16 cm.sup.-3, and N-type semiconductor region 806 which forms horizontal charge transfer elements 704a and 704b and has an impurity concentration of approximately 1E17 cm.sup.-3 are formed on P-type well layer 802. Further, charge transfer electrodes 808a, 808b, 808c and 808d of vertical charge transfer elements 702 driven by charge transfer pulse signals .phi.V.sub.1, .phi.V.sub.2, .phi.V.sub.3 and .phi.V.sub.4 applied thereto and charge transfer electrodes 811a, 811b, 811c and 811d of first and second horizontal charge transfer elements 704a and 704b driven by charge transfer pulse signals .phi.H.sub.1, .phi.H.sub.2, .phi.H.sub.3 and .phi.H.sub.4 applied thereto, respectively, which are all formed from, for example, a polycrystalline silicon film of two layers, are disposed on the surface of N.sup.- -type semiconductor substrate 801 with insulation film 807 interposed therebetween.
Such a conventional solid state image device as described above is characterized in that, since a bidirectionally transferable charge transfer apparatus is employed for vertical charge transfer element 702 set and horizontal charge transfer elements 704a and 704b, the scanning direction of an imaging screen can be changed arbitrarily by changing over the combination of transfer pulse signals to be applied to the charge transfer electrodes by an external circuit.
When the transfer direction of vertical charge transfer element 702 set is selected to the downward direction in FIG. 1 and the transfer direction of horizontal charge transfer element 704a is simultaneously selected to the leftward direction in FIG. 1, signal charge stored in photoelectric transform element 703 set in response to an amount of incoming light is first read out to charge transfer electrodes 808a or 808c of corresponding vertical charge transfer element 702 set and then transferred successively in the downward direction in FIG. 1 in parallel in vertical charge transfer element 702 set, and then it is successively transferred to horizontal charge transfer element 704a. The signal charge sent to horizontal charge transfer element 704a is successively transferred in the leftward direction in FIG. 1 and outputted as a video signal from output terminal 707a via outputting circuit element 706a.
In this instance, screen scanning exhibits a mode in which horizontal scanning in the rightward direction in FIG. 1 beginning with the left lower corner of FIG. 1 is successively repeated for each one horizontal scanning period in the upward direction of FIG. 1 (the mode is hereinafter referred to as mode A).
If, from the condition described above, only the transfer direction of horizontal charge transfer element 704a is changed over to the rightward direction in FIG. 1, then screen scanning of the video signal outputted from output terminal 707b exhibits another mode wherein horizontal scanning to ward the left side in FIG. 1 beginning with the right lower corner of FIG. 1 is successively repeated for each one horizontal scanning period in the upward direction in FIG. 1 (the mode is hereinafter referred to as mode B).
Similarly, if the transfer direction of vertical charge transfer element 702 set is selected to the upward direction in FIG. 1 and the transfer direction of horizontal charge transfer element 704b is simultaneously selected to the leftward direction in FIG. 1, then screen scanning of the video signal outputted from output terminal 707c exhibits a further mode wherein horizontal scanning in the rightward direction in FIG. 1 beginning with the left lower corner of FIG. 1 is successively repeated for each one horizontal scanning period in the downward direction in FIG. 1 (the mode is hereinafter referred to as mode C).
Further, if, from the condition described above, only the transfer direction of second horizontal charge transfer element 704b is changed over to the rightward direction in FIG. 1, then screen scanning of the video signal outputted from output terminal 707d exhibits a still further mode wherein horizontal scanning toward the left side in FIG. 1 beginning with the right lower corner of FIG. 1 is successively repeated for each one horizontal scanning period in the downward direction in FIG. 1 (the mode is hereinafter referred to as mode D).
In a video camera which employs such a conventional solid state imaging device as described above, if the screen scanning mode of the video camera is set to the mode A and the positional relationship between the video camera and an object of imaging is adjusted so that a reproduced image by the image signal outputted from output terminal 707a then is an erected image in both of the upward, downward and leftward, rightward directions, then in the mode B, a reproduction image by the video signal outputted from output terminal 707b is an erected image in the upward and downward directions but is an inverted image in the leftward and rightward directions, but in the mode C, a reproduction signal by the video signal outputted from output terminal 707c is an erected image in the leftward and rightward directions but is an inverted image in the upward and downward directions. Further, in the mode D, a reproduction image by the video signal outputted from output terminal 707d is an inverted image in both of the upward and downward directions and the leftward and rightward directions.
While, in the conventional example described above, horizontal charge transfer elements 704a and 704b allow transfer in both directions, where horizontal charge transfer elements 704a and 704b otherwise allow transfer only in one direction, only the mode A and the mode C or the mode B and the mode C are available.
The solid state imaging device shown in FIGS. 3 and 4a to 4d is of the interline transfer type and has horizontal charge transfer elements at the opposite ends of vertical charge transfer elements.
Referring to FIG. 3, when the transfer direction in first vertical charge transfer element 702a set on the lower side of FIG. 3 with respect to a boundary between first and second vertical charge transfer elements 702a and 702b while the transfer direction in second vertical charge transfer element 702b set on the upper side of FIG. 3 and the transfer directions in first and second horizontal charge transfer elements 704a and 704b are simultaneously selected to the leftward direction in FIG. 3, signal charge stored in photoelectric transform element 703 set in response to the amount of incoming light is first read out to charge transfer electrodes 808a or 808b of corresponding first and second vertical charge transfer elements 702a and 702b. Then, in first vertical charge transfer element 702a set, the signal charge is successively transferred in the downward direction in FIG. 3 in parallel to horizontal charge transfer element 704a, and the signal charge sent to first horizontal charge transfer element 704a is successively transferred in the leftward direction in FIG. 3 and outputted as a video signal from output terminal 707a via the corresponding outputting circuit element, but in second vertical charge transfer element 702b set, the signal charge is successively transferred in the upward direction in FIG. 3 in parallel to second horizontal charge transfer element 704b, and the signal charge sent to horizontal charge transfer element 704b is successively transferred in the leftward direction in FIG. 3 and outputted as a video signal from output terminal 707c via the corresponding outputting circuit element.
In this instance, since video signals for one screen can be outputted in parallel from output terminals 707a and 707c, a mode wherein screen scanning can be performed at a high speed is exhibited (the mode is hereinafter referred to as mode E).
Such a solid state imaging device as described above is characterized in that, when compared with the solid state imaging device shown in FIGS. 1 and 2a to 2d, screen scanning can be performed at a higher speed since it includes first and second vertical charge transfer element 702a and 702b sets formed from a plurality of columns of bidirectionally transferable charge transfer apparatus and signal charge can be outputted in parallel from output terminal 707a and output terminal 707c.
In the solid state imaging device shown in FIG. 5, since first element separation region 701 and vertical charge transfer elements 702 contact with each other on the opposite side to a side on which horizontal charge transfer element 704 is provided, a reference potential is supplied to first element separation region 701 via second element separation region 705 which is fixed to the reference potential via a metal wiring line at a peripheral portion of the device.
However, in such a solid state imaging device wherein horizontal charge transfer elements are provided at the opposite ends of vertical charge transfer elements as described above, since it does not have a portion at which first element separation region 701 and second element separation region 705 contact with each other, first P.sup.+ -type semiconductor region 803 which forms first element separation region 701 and has an impurity concentration of approximately 1E18 cm.sup.-3 and second P.sup.+ -type semiconductor region 804 which forms second element separation region 705 and has an impurity concentration of approximately 1E18 cm.sup.-3 are electrically connected to each other via P-type well layer 802 which has an impurity concentration of approximately 5E15 cm.sup.-3. However, since P-type well layer 802 has an electric resistance much higher than the electric resistance of first P.sup.+ -type semiconductor region 803 which forms first element separation region 701 or second P.sup.+ -type semiconductor region 804 which forms second element separation region 705 (for example, the electric resistance of P-type well layer 802 is approximately 50 to 100 k.OMEGA./.quadrature., and the electric resistances of first and second P.sup.+ -type semiconductor regions 803 and 804 are approximately 0.5 k.OMEGA./.quadrature.), the potential of first element separation region 701 is unstable.
Further, the solid state imaging apparatus has another problem in that, since a pulse signal for charge transfer is applied to charge transfer electrodes 808 which form vertical charge transfer elements 702, the potential of first element separation region 701 is fluctuated by an influence of the charge transfer pulse signal, resulting in reduction of the maximum handling charge amount of vertical charge transfer elements 702, deterioration of the transfer efficiency and so forth.